<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Margenes de la pagina web</title>
<style type="text/css">
body{
  margin-left: 0px;
  margin-right: 10px;
  margin-top: 0px;
  margin-bottom: 10px;
}
.micapa{
  background-color: #f00;
  width: 100%;
  height: 100%;
}
</style>
</head>
<body>

<div class="micapa">
Texto
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Texto
</div>

</body>
</html>